1. Field of the Invention
The present invention generally relates to the utilization of ultraviolet (UV) light for the disinfection of water and other liquids, and specifically to the incorporation of a UV light detection system in a water disinfection unit.
2. Description of the Related Art
It has long been known to disinfect drinking water and other liquids by exposure to UV light. In fact, the first devices for doing so (xe2x80x9cUV water disinfection unitsxe2x80x9d or, alternatively, xe2x80x9cUV water disinfectorsxe2x80x9d) were developed in the early nineteen hundreds. Unfortunately, these early systems proved to be unreliable, impractical, and expensive, and were rapidly displaced by more attractive approaches, such as chlorination. However, UV technology has matured considerably since then and has become less expensive and more reliable. Also, health concerns about standard chlorine disinfection have accelerated the increasing popularity of UV water disinfection, particularly in Europe. By 1990, approximately 2000 municipal water treatment plants in Europe were using UV disinfection systems.
Most modern UV water disinfectors employ a construction wherein water is disinfected as it flows under a UV lamp. An exemplary device for cost-efficient, small-scale use is disclosed in U.S. Pat. No. 5,780,860 to Gadgil et al. Gadgil et al. teaches a highly effective, practical, and maintenance-free UV disinfection system, utilizing gravity-driven liquid delivery and treatment with a UV lamp.
A major concern with use of UV water disinfectors is the potential risk of output water that is not completely disinfected. Particularly in developing countries, many lives are lost annually due to the consumption of infected drinking water. Successful disinfection depends upon the intensity of the UV light, the turbidity and flowrate of the water as it passes underneath the UV lamp. If the UV light intensity is too low, the water will not receive enough UV energy for complete disinfection. Similarly, if the flowrate is too high, the water will not absorb enough UV energy as it passes under the lamp. Thus, there must be a balancing of the UV light intensity and the water flowrate. For a given system, if the UV light intensity is decreased, then so must be the flowrate. Conversely, if the flowrate is increased, then so must be the UV light intensity.
It is beneficial to include safety features in UV water disinfectors to prevent the delivery of water that is not successfully disinfected. For example, the system of Gadgil et al. illustrates the use of a solenoid valve electronically wired to close automatically and discontinue the flow of water to the UV lamp region if there is a stoppage of power to the UV lamp. In other words, the solenoid valve will shut off the entire system if there is a power outage or if the lamp bulb fuses. This feature is particularly advantageous for UV water disinfectors used in developing countries, where power outages are more frequent.
Another desirable safety feature is the utilization of UV light sensors to measure and monitor the intensity of the UV light exposed to the water. For any desired water flowrate, the UV light intensity received by the water can be readily determined by using fundamental principles of physics and mathematics. For successful disinfection, the UV light intensity must be maintained above a minimal level relative to the turbidity and flowrate. The sensors are provided to notify the system whenever the intensity drops dangerously close to the minimum intensity, which might occur if the power source to the UV lamp provides a fluctuating load. Typically, the system is designed to shut off in such a case, by utilizing some means for stopping the flow of water through the system, such as a solenoid valve as taught by Gadgil.
The turbidity of the water also affects the required level of UV light intensity for safe disinfection. For cloudy input water, a higher UV light intensity is required for complete disinfection. This is because, in more turbulent flows, the UV light is absorbed over a shorter distance.
Sensors used in UV water disinfectors are typically vacuum photodiodes constructed to be sensitive to UV light. This sensor includes two electrodes separated by a vacuum chamber, commonly enclosed within a quartz envelope. UV light striking the light-sensitive material causes electrons to shoot through the vacuum and generate an electric current directly proportional to the UV light intensity. The electrons are accelerated through the vacuum by application of an electric field between the electrodes. Using well known methods, this current signal is normally converted to a voltage output signal to indicate UV light intensity.
Unfortunately, the vacuum photodiode entails several disadvantages, particularly in the context of UV disinfection. One disadvantage is that the vacuum chamber and separated electrodes result in a relatively large size and high cost. Another disadvantage is that this sensor is relatively expensive, costing within the range of $50-$100. Another disadvantage is that the quartz envelope is very delicate and must be protectively encased, most commonly in epoxy and metal. This further adds to the cost of the sensor and, consequently, of the entire UV disinfection system. Furthermore, the delicateness of the vacuum photodiode results in a limited lifespan, normally less than five years. This necessitates frequent replacement and further adds to the operational costs. Another disadvantage of the vacuum photodiode is that it is less sensitive to fluctuations in UV light intensity. This results in relatively imprecise measurements thereof and thus adds to the uncertainty of the entire disinfection process.
Thus, there is a need for a more optically and mechanically stable, longer lasting, and less expensive method of sensing the amount of UV light intensity exposed to the water flowing through a UV water disinfector.
Accordingly, it is a principle object and advantage of the present invention to overcome some or all of these limitations and to provide an improved UV light sensor for a UV liquid disinfector.
In accordance with one aspect of the invention, an ultraviolet light detector is provided for detecting a level of ultraviolet light exposed to a liquid flowing within an ultraviolet liquid disinfection unit. The detector includes a first photodetector and a second photodetector. The first photodetector is configured to generate a first electric signal proportional to a level of a first spectrum of light, including ultraviolet light. The second photodetector is configured to generate a second electric signal proportional to a level of a second spectrum light, substantially including the first spectrum except for a range of ultraviolet light. The first and second electric signal are connected to generate an output electric signal that is equal to the difference between them, so that the output electric signal is proportional to a level of the range of ultraviolet light. In the illustrated embodiment, the output electric current is converted to a voltage and/or used to control various elements within the disinfection unit, such as an alarm and/or a solenoid valve configured to shut off the system.
In accordance with another aspect of the invention, a method is provided for detecting the amount of ultraviolet light in an ultraviolet liquid disinfection unit. According to this method, a first photo-induced electric current is generated. This current is proportional to the amount of a first spectrum of light exposed to liquid within the unit, including a range of ultraviolet light. A second photo-induced electric current is also generated. This current is proportional to the amount of a second spectrum of light exposed to the liquid. The first and second photo-induced electric currents are connected together to generate an output electric current proportional to the amount of the range of ultraviolet light exposed to the liquid.
In accordance with another embodiment of the invention, an ultraviolet disinfection unit is disclosed. The unit includes a liquid flow path and an ultraviolet lamp positioned to irradiate liquid within the flow path. A first photo detector is configured to generate a first electric signal, which is indicative of an amount of a first spectrum of light irradiating the liquid. A second photo detector is configured to generate a second electric signal, which is indicative of an amount of a second spectrum of light irradiating the liquid, where the second spectrum is not equal to the first spectrum. A circuit combines the first and second signals to generate an output signal, which indicates an amount of a range of ultraviolet light irradiating the liquid.